If I have say 2 * sig^2 /. rl, I get 2 * var. What can I do to get directly the evaluation 0.4 ?

For now, I apply rl twice like in (2 * sig^2 /. rl) /.rl but is it possible to have directly the right value (here, I want sig to be the square root of whatever value var holds/is transformed into) from a transformation rule ?